The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An ultrasonic flow sensor measures the average velocity of liquid or gaseous media by means of ultrasonic transducers based on the principle that the transit time of an ultrasonic wave from the transmitter of a transducer to the corresponding receiver is determined by the fluid velocity and the ultrasonic wave propagating direction. Normally, a pair of transducers is used, one is installed in upstream and the other is installed in downstream. Each transducer can be used as a transmitter or a receiver. One ultrasonic pulse is transmitted from the upstream transducer to the downstream transducer. The second ultrasonic pulse is transmitted from the downstream transducer to the upstream transducer. The transit time in each direction is accurately measured by an electronic console. The difference of the two transit-time data is proportional to flow velocity. It is then used to calculate the average flow velocity of the fluid.
The following three factors are most important criteria when customers select ultrasonic flow sensors for their applications: 1) measurement accuracy, 2) measurement reliability, and 3) the cost of ownership. Ultrasonic flow sensors with high measurement accuracy and reliability as well as low cost of ownership are the choice of the majority of customers.
The measurement accuracy and reliability of an ultrasonic flow sensor are mainly affected by: 1) the flow velocity of the fluid to be measured, 2) the uniformity of the velocity profile, 3) the signal strength of the measuring ultrasound wave, and 4) the parasitic multi-mode acoustic wave generated by the internal reflection.
In general the flow velocities, the uniformity of the velocity profile and the ultrasonic signal strength have positive impact on the measurement accuracy and reliability of an ultrasonic flow sensor. Higher flow velocity, lesser disturbance, better uniformity of the velocity profile and stronger ultrasound signal lead to higher measurement accuracy and reliability. On the other hand, the parasitic multi-mode ultrasonic wave generated by the internal reflection has negative impact on measurement accuracy and reliability. The stronger the parasitic multi-mode ultrasonic wave, the lower the measurement accuracy and reliability.
The cost of ownership of ultrasonic flow sensors depends on the initial product price and its life cycle. A competitive ultrasonic flow sensor must be easy to manufacture, easy to assemble, and have to maintain performance stability over its life cycle. This in turn requires that an ultrasonic flow sensor must be as simple as possible and have minimal number of components and/or parts.